British police are launching a new investigation into the disappearance of little Madeleine McCann six years ago and believe she may still be alive.

Scotland Yard is launching a new investigation into the case after finding fresh leads and identifying potential persons of interest they want to interview.

Maddie McCann was 3 when she vanished from a holiday apartment in Portugal in 2007 as her parents ate dinner at a nearby restaurant with friends. Her disappearance sparked a global hunt for the toddler, but an investigation by Portuguese police was shelved in July 2008.

British detectives will now carry out their own investigation after uncovering what they say is new evidence and carrying out new witness interviews. They believe Madeleine may still be alive, having found no evidence to prove otherwise during a two year review of the case.

Madeleine's parents Kate and Gerry McCann say the decision to launch a new investigation is "a big step forward."

Thirty-eight "persons of interest" from a number of European countries have been identified by Scotland Yard. Twelve of those are British nationals believed to have been in Portugal when Madeleine went missing, but not all of them are currently living in the UK.

Detectives will investigate whether those individuals were involved in Madeleine's disappearance. None of the McCanns' friends who were having dinner with them on that night are among the 38.

"Kate and Gerry warmly welcome the shift from review to investigation," the family's spokesman told ABC News. "It is clearly a big step forward in establishing what happened and, hopefully, towards bringing whoever is responsible for Madeleine's abduction to justice."

During their review of the case, British officers looked at material from the Portuguese investigation, UK law enforcement agencies, and several private investigation agencies. Detective Chief Inspector Andy Redwood, who is leading the probe, said this puts them in a "unique position" to solve the case.

"That has given us the ability to see this case with fresh eyes, and through that bring out new, genuinely new, lines of inquiry. And I'm hopeful when we pursue those lines of inquiry that we will be able to bring some sort of resolution," Redwood said.

Police in Portugal have not reopened the case since it was closed in 2008. British detectives will be returning there as part of this new investigation.

Madeleine's family marked what would have been her 10th birthday on May 12 of this year.